Dear Google Answers:

It is my understanding that the sender of an SMS text message can
easily be spoofed.  See here for example:

http://www.asianlaws.org/cert/sms_spoofing.htm

That is, as a recipient of a text message on my mobile phone I cannot
be certain who the sender really is.  If this is indeed true, then my
question is? has any work been done to provide authentication
mechanisms for SMS?

A good answer will illuminate what are the spoofing risks in SMS, what
has already been done (i.e., state-of-the-art) to minimize these
risks, and what possibly could be done.

Thanks!

In my limited knowledge of the subject, as far as I understand it is
impossible to spoof sms messages from a mobile device and it can only
be done via the internet through devices networked to sms gateways.

An example of this would be the www.sms.ac service, which allows users
to send messages via the internet. The authentication mechanism that
you speak of in this instance is a text message 'pin code' sent to the
users mobile phone, which they then have to input into a secure web
page to confirm that that mobile phone number is theirs before being
allowed to send messages.

Some services used to exist which didn't bother doing this (eg.
www.redcoal.com) and one could send text messages seemingly appearing
from whichever mobile number the user placed in the "from" field.
However, I believe they have now wisened up to this.

So in short, work has been done to provide authentication mechanisms for SMS.

Thank you for the comment.  Spoofing via the Internet is a concern. 
Imagine if someone could spoof a traffic alert... then they could
create traffic jams.  You can imagine worse situations too, I am sure.
 Here is an example:

http://infotech.indiatimes.com/articleshow/776694.cms

Thanks!